This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP99/04668 which has an International filing date of Aug. 27, 1999, which designated the United States of America.
The present invention relates to a process for producing a material for organic electroluminescence device by implanting or injecting an emission center-forming compound through molecular implantation with laser, a material for organic electroluminesdence device obtained by this process, and to an organic electroluminescence device (elements) produced with this organic electroluminescence device material.
Electroluminescence devices (hereinafter, sometimes referred to simply as EL devices) have generally been classified as inorganic EL devices or organic EL devices according to what they are made from. On one hand some inorganic EL devices utilizing inorganic fluorescent molecules are already in practical use, and have been brought into application to the backlight of clocks or the like, while on the other hand organic EL devices have been desired to be brought into practical use because of their excellence in brightness or luminance, efficiency, and high-speed responsivity.
Electroluminescence devices are made from a compound or compounds having an electron-transporting function, a hole-transporting function, and an emission center-forming function. As for their structures, there have been reported devices of the single-layer type having a single layer provided with all the functions mentioned above, and devices of the multilayer-type composed of layers having different functions. The principle of light emission is considered to be based on the phenomenon that electrons or holes injected from a pair of electrodes recombine within a light-emitting layer to form excitons, which excite the molecules of a light emissive material for the light-emitting layer.
As a compound constituting each layer, a low-molecular weight compound of high light-emission efficiency, a macromolecular compound having high physical strength, or the like is employed. However, when a low-molecular weight compound is used, a film is formed by means of a vapor deposition technique which is inferior in productivity, while a macromolecular compound is formed into a film by coating or applying a solution and thus capable of being formed into films of larger sizes.
Japanese Patent Application Laid-Open No. 96959/1996 (JP-A-8-96959) and Japanese Patent Application Laid-Open No. 63770/1997 (JP-A-9-63770) disclose organic EL devices comprising a single light-emitting layer made of a polymer binder within which varieties of fluorescent dyes (or colorants, pigments) are dispersed, the polymer binder having both electron-transporting function and hole-transporting function. Each of these organic EL devises is reported to present, as a whole, white light due to the light emission of each light-emitting compound independent of one another. Moreover, as compared with organic EL devices of the multilayer-type, those of the single-layer type are hardly deteriorated in light-emission intensity.
Fine patterning, particularly multicolor patterning (full-coloration) of these organic EL devices is difficult because, in their fabrication, a film is formed by means of a solution coating technique in which a solution of a polymer binder and a fluorescent dye(s) dispersed in a specific solvent is applied onto a substrate.
As multicolor patterning methods, a color filer method, a color-converting method, the ink-jet method by T. R. Hebner (Appl. Phys. Lett. 72,5 (1998), p.519), the photobleaching method by Kido, et al, and others have been reported.
The color filter method or color-converting method has the advantage of not requiring the patterning of a light-emitting layer, but suffers deterioration in conversion efficiency caused by the use of a filter. In the ink-jet method, a pattern formed by ink-jet printing shows a center-raised, i.e., conical profile and is inferior in smoothness of its surface, resulting in difficulty in uniformly providing electrodes thereon. Moreover, the cross section of the pattern is desired to be rectangular, but that of a pattern by ink-jet printing cannot be formed so and is circular. Further, the dimensions of a pattern largely depends on conditions under which the pattern is dried and the concentration of the solution. In the photobleaching method, only a special emission center-forming compound which loses its fluorescence upon UV oxidation is employable and therefore colors expressable by EL devices are limited.
As was described above, in conventional film-forming methods by solution coating, although it is possible to use a macromolecular compound of high physical strength, it is difficult to provide fine patterns. In addition to that, also in the above-described patterning methods, compounds available for these methods are limited, and films having surface smoothness suitable for organic EL devices cannot be obtained.
As the molecular implantation technique, Japanese Patent Application Laid-Open No. 297457/1994 (JP-A-6-297457) discloses a method comprising a step of, with (A) a functional material or a solid material containing a functional material and (B) a solid material into which a functional component is to be implanted placed such as to face each other, irradiating a laser pulse thereby to implant the functional component into the solid material. Japanese Patent Application Laid-Open No. 106006/1996 (JP-A-8-106006) discloses a method comprising the steps of bringing a source film of an organic macromolecular compound within which dyes absorptive of a pulse laser are dispersed into tight contact with a target film of an organic macromolecular compound transmittable of a pulse laser, and irradiating a pulse laser from the target film side at an intensity of or below the ablation threshold value of the source film thereby to implant the dyes into the target film. This literature says that the molecular implantation technique can be utilized in the fabrication of color filters for displays or the like.
Accordingly, an object of the present invention is to provide a material for organic EL device (particularly, organic EL device-use films) that can be fine-patterned even when a macromolecular compound is used as an EL device material, and a process for producing the same.
Another object of the present invention is to provide a material for organic EL device which is excellent in surface smoothness and has good contactness with electrodes, and an organic EL device using the same.
The inventors of the present invention made intensive and extensive studies to achieve the above objects, and finally found that a molecular implantation technique using a laser makes it possible to implant an emission center-forming compound(s) with ease even in the case of injection into a macromolecular compound, and provide organic EL devices that can be finely and minutely patterned.
That is, the production process of a material for organic EL device of the present invention comprises the steps of
bringing a source (A) containing an emission center-forming compound absorptive of a laser beam into contact with a target (B) which is transmittable of the laser beam and has at least one function selected from an electron-transporting function and a hole-transporting function, and
irradiating the laser beam from the source (A) side or the target (B) side at an intensity of or below the ablation threshold (value) of the source (A) thereby to implant the emission center-forming compound into the target (B), providing a material for organic electroluminescence device having luminescence (emission) centers. The target may be an organic polymer having at least one function selected from the electron-transporting function and the hole-transporting function (e.g., poly-N-vinylcarbazol) or may comprise a compound having at least one function selected from the electron-transporting function and the hole-transporting function and an organic polymer having film-forming properties or film-formability.
The organic EL device material may be in the form of a film, and the laser beam may be a pulse laser beam (pulsed laser) having a pulse width of 10 Ps to 10 xcexcs. The laser beam diameter may be 1 xcexcm to 5 mm.
The present invention includes a material for organic EL device obtained in accordance with the process described above, and an organic EL device (element) formed with this organic EL device material.